Thermal printhead and protection cover mounted on the same

ABSTRACT

A thermal printhead (10) includes an insulating head substrate (11) having a first edge (11a) and a second edge (11b) opposite to the first edge, a heating resistor (12) formed on the head substrate (11) along the first edge (11a), at least one drive IC (13) mounted on the head substrate (11) along the second edge (11b), and a protection cover (20) mounted for covering the drive IC (13). The protection cover (20) includes a cover member (22) for covering the drive IC (13) and a fixation member (21) formed integrally with the cover member (22). The fixation member (21) has a positioning wall (23) coming into direct contact with the second edge (11b) of the head substrate (11). The fixation member is designed to attach the protection cover (20) to the head substrate (11) without utilizing separate fixing means.

TECHNICAL FIELD

The present invention relates to a thermal printhead and a protectioncover mounted on the same.

BACKGROUND ART

A typical thermal printhead includes an insulating head substrate formedwith a heating resistor and drive ICs for actuating the heatingresistor. The head substrate is mounted on a supporting member which ismade of aluminum for example and has good thermal conductivity.

Taking a thick film-type thermal printhead for example, a narrowstrip-like heating resistor is formed on a substrate by a thick filmprinting method. The narrow strip-like heating resistor islongitudinally sectionalized into tiny regions to provide heating dots.These heating dots are electrically connected, via a plurality ofindividual electrodes, to output pads of drive ICs. Further, the heatingdots are equally connected to a common electrode. Each output pad of adrive IC is connected to an individual electrode by a bonding wire.

The drive ICs and the bonding wires are enclosed by a hard protectioncoating made of a thermosetting resin such as an epoxy resin forexample. Main functions of the protection coating are to protect thedrive ICs and wire-bonded portions from external mechanical forces andto prevent static electricity from destroying the drive ICs. The reasonsuch a preventive measure is necessary to be taken for the drive ICs isthat the static electricity, which is generated on the recording paperdue to the sliding contact between the recording paper and the heatingresistor during printing operation, may be discharged to the drive ICsand destroy them.

In the field of thermal printheads, high-speed printing has beenincreasingly required. To meet this requirement means to increase thespeed of sliding movement of the recording paper relative to the heatingresistor. As a result, a greater amount of static electricity will begenerated on the recording paper during the printing operation, and thedischarge may eventually become unbearable to the protection coating.

To cope with such a problem, conventionally, a protection cover may beadditionally provided for covering a protection coating which enclosesdrive ICs and bonding wires. Such a protection cover prevents theelectrostatically charged recording paper from coming into directcontact with the protection coating.

Many conventional protection covers are mounted on thermal printheads byusing fixing means such as screws (see U.S. Pat. No. 4,963,886). Withsuch an arrangement, a protection cover is usually attached to asupporting member of the thermal printhead or to a printed circuit boardfor external connection. To fix the protection cover by fixing meanssuch as screws is a troublesome operation, and it is difficult to locatethe protection cover with satisfactory accuracy. Further, the error inattaching the supporting member to the head substrate is additional tothe error in attaching the printed circuit board for external connectionto the head substrate. Therefore, the positioning accuracy of theprotection cover relative to the heating resistor of the head substratecannot be improved beyond a certain level.

DISCLOSURE OF THE INVENTION

Therefore, it is an object of the present invention to provide aprotection cover for a thermal printhead, which is attached to a headsubstrate with ease and high positional accuracy.

It is another object of the present invention to provide a thermalprinthead carrying such a protection cover.

According to a first aspect of the present invention, there is provideda thermal printhead including an insulating head substrate having afirst edge and a second edge opposite to the first edge, a heatingresistor formed on the head substrate along the first edge, at least onedrive IC mounted on the head substrate along the second edge, and aprotection cover mounted for covering the drive IC. The protection coverincludes a cover member for covering the drive IC and a fixation memberformed integrally with the cover member. The fixation member has apositioning wall coming into direct contact with the second edge of thehead substrate. The fixation member is designed to attach the protectioncover to the head substrate without utilizing separate fixing means.

According to a preferred embodiment of the present invention, thefixation member of the protection cover is made in a form of a channelgroove having a pair of elastically deformable clip pieces projectingfrom the positioning wall toward the head substrate. A minimum distancebetween the clip pieces in an original state is set to be smaller than athickness of the head substrate so that the second edge of the headsubstrate is clipped by the clip pieces. Thus, the assembling operationof the protection cover can be performed with remarkable ease, andadaptation to automatic assembling is easily realized, as opposed to anattaching manner which requires separate fixing means such as screws ortools.

The protection cover of the above embodiment is attached to the headsubstrate, unlike the prior art wherein a supporting member or printedcircuit board for external connection is utilized for attachment. Thus,it is possible to attain a high positioning accuracy of the covermember, in particular, relative to the heating resistor on the headsubstrate. The transferring path for recording paper in the printingunit utilizing a thermal printhead is mainly determined by a platenarranged in facing relation to the heating resistor on the headsubstrate. Ideally, the position of the platen should be determinedbased on that of the heating resistor on the head substrate inparticular. In the above embodiment, as already described, the positionof the cover member of the protection cover is determined relative tothe head substrate. Thus, in the above embodiment, it is easy to performan ideal and accurate positioning of the cover member relative to thetransferring path of the recording paper. As a result, while it ispossible to minimize the uneven contacting of the recording paper withthe protection cover, the projection length of the cover member can bemaximized so that the protection cover properly and fully serves toprotect the drive ICs and guide the recording paper.

In the preferred embodiment described above, one of the clip pieces hasa flat contact surface held in surface contact with an obverse surfaceof the head substrate, while the other clip piece has a convexly curvedportion held in contact with a reverse surface of the head substrate.Such features are advantageous in making the attachment reliable andstable.

Further, in the above preferred embodiment, advantageously, the headsubstrate is mounted on an electrically conductive supporting memberhaving a high thermal conductivity, the protection cover iselectrostatically conductive, and a portion of the fixation member ofthe protection cover contacts the supporting member. With such anarrangement, the printing performance of the thermal printhead isimproved due to a proper heat-dissipating function of the supportingmember. Further, the static electricity generated on the recording paperduring high-speed printing operation for example can be lead to theconductive supporting member via the protection cover. As a result, thedrive ICs on the head substrate are advantageously prevented frombreaking down due to the discharge of the static electricity.

The protection cover may be integrally formed by a carbon-containingsynthetic resin to provide an electrostatic conductivity.

According to another preferred embodiment of the present invention, thehead substrate is mounted on an electrically conductive supportingmember having a high thermal conductivity, and the fixation member ofthe protection cover is made in a form of a frame which includes anengaging front wall coming into engagement with an edge of thesupporting member adjacent to the heating resistor, and a pair of sidewalls connecting the engaging front wall to the positioning wall. Inthis embodiment again, the cover member of the protection cover isaccurately positioned relative to the head substrate by the positioningwall.

Since there is no need to use separate fixing means such as screws, theattachment of the protection cover is easily performed.

In the above-mentioned second preferred embodiment, the positioning wallpreferably includes a step portion engaging the obverse surface of thehead substrate adjacent the second edge of the head substrate. Asalready described, the inconvenience caused by the accumulation ofstatic electricity is eliminated, if the protection cover is integrallyformed by an electrostatically conductive material such as acarbon-containing synthetic resin.

According to still another preferred embodiment of the presentinvention, the drive ICs on the head substrate are enclosed by a hardprotection coating, while the cover member of the protection cover,which is elastically deformable, comes into elastic contact with theprotection coating. With such an arrangement, the cover member of theprotection cover is always held in elastically close contact with thehard protection coating enclosing the drive ICs. Therefore, it ispossible to advantageously prevent a transfer error of the recordingpaper, which otherwise might be caused by the recording paper entering aclearance between the cover member and the protection coating.

According to a second aspect of the present invention, there is provideda protection cover mounted on a thermal printhead including aninsulating substrate having a first edge and a second edge opposite tothe first edge, a heating resistor formed on the head substrate alongthe first edge, and at least one drive IC disposed on the head substratealong the second edge. The protection cover including a cover member forcovering the drive IC, and a fixation member formed integrally with thecover member.

The fixation member has a positioning wall coming into direct contactwith the second edge of the head substrate. The fixation member isattached to the head substrate without utilizing separate fixing means.

Other objects, features and advantages of the present invention will beclearer from the detailed explanation of the embodiments described belowwith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a thermal printhead accordingto a first embodiment of the present invention;

FIG. 2 is an exploded perspective view of the same thermal printhead;

FIG. 3 is an enlarged plan view showing a heating portion of the samethermal printhead;

FIG. 4 illustrates the same thermal printhead in operation;

FIG. 5 is a cross-sectional view showing a thermal printhead accordingto a second embodiment of the present invention;

FIG. 6 illustrates the thermal printhead shown in FIG. 5 in operation;

FIG. 7 is a cross-sectional view showing a thermal printhead accordingto a third embodiment of the present invention;

FIG. 8 is an exploded perspective view of the same thermal printhead;

FIG. 9 illustrates the thermal printhead shown in FIG. 7 in operation;and

FIG. 10 is a cross-sectional view showing a thermal printhead accordingto a fourth embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS. 1-3 show a thermal printhead according to a first embodiment ofthe present invention.

The thermal printhead according to the first embodiment, which isgenerally indicated by reference numeral 10, has a basic structuresimilar to that of a typical thick film-type thermal printhead.Specifically, the thermal printhead 10 includes an elongated rectangularhead substrate 11 made of an insulating material such asalumina-ceramic. The upper surface of the head substrate 11 is formedwith a heating resistor 12 and drive ICs 13 for actuating the heatingresistor 12. The heating resistor 12 is formed into a narrow stripextending along the first edge 11a of the head substrate 11 by a thickfilm printing method using a resistor paste such as ruthenium oxidepaste.

The upper surface of the head substrate 10 is formed with a commonelectrode 14 between the first longitudinal edge 11a and the heatingresistor 12. As fully shown in FIG. 3, the common electrode 14 hascomb-tooth portions 14a extending under the heating resistor 12. Theupper surface of the head substrate 10 is also formed with a comb-teethlike individual electrodes 15 extending under the heating resistor 12.The respective regions of the heating resistor 12 which aresectionalized by adjacent comb-tooth portions 14a of the commonelectrode 14 function as heating dots 16. When a selected individualelectrode 15 is turned on for actuation by a drive IC 13 describedhereinafter, a current passes across a corresponding heating dot 16 (theshaded portion shown in FIG. 3, for example) for generation of heat.

The drive ICs 13 are linearly arranged along the second longitudinaledge 11b of the head substrate 11. The respective individual electrodes15 extend toward the second longitudinal edge 11b of the head substrate11 for connection to corresponding output pads (not shown) of the driveICs 13 via bonding wires 17a.

Power pads (not shown) and signal pads (not shown) of the drive ICs 13are also connected, via bonding wires 17b, to a predetermined wiringpattern (not shown) formed on the head substrate 11.

The linearly arranged drive ICs 13 together with the bonding wires 17a,17b for electrical connection are enclosed by a hard protection coating18. The protection coating 18 is made of a thermosetting resin such asan epoxy resin for example. Specifically, the resin in a liquid state isapplied to enclose the drive ICs 13 and then cured under heating.

The head substrate 11 is attached to the supporting member 19 via anadhesive for example. At this time, the head substrate 11 is attached tothe supporting member 19 so that a predetermined distance L is providedbetween a longitudinal edge 19a of the supporting member 19, which isadjacent to the first longitudinal edge 11a of the head substrate 11,and the heating resistor 12. Thus, the heating resistor 12 of the headsubstrate 11 is positioned with fairly great accuracy relative to thelongitudinal edge 19a of the supporting member 19. The supporting member19, which is made of a material having good thermal and electricalconductivities such as aluminum for example, also functions as a heatsink plate.

The drive ICs 13 are covered by the protection coating 18 as well as theprotection cover 20. As clearly seen from FIG. 1, the protection cover20 includes a channel groove-shaped fixation member 21 held in clippingengagement with the other edge 11b of the head substrate 11, and a covermember 22 extending from the fixation member 21 to cover the upper sidesof the drive ICs 13. The protection cover 20 may be integrally producedby extruding a resin for example.

The channel groove-shaped fixation member 21 of the protection cover 20includes a pair of vertically spaced projections of clip pieces 24, 25,which are formed integrally with a vertical positioning wall 23 cominginto direct contact with the second longitudinal edge 11b of the headsubstrate 11. The upper clip piece 24 has a flat contact surface 24aheld in close contact with the upper surface of the head substrate 11,while the lower clip piece 25 has an upwardly convex curved portion 25a.The distance L₁ between the contact surface 24a of the upper clip piece24 and the convex curved portion 25a of the lower clip piece 25 is setto be smaller than the thickness L₂ of the second longitudinal edge 11bof the head substrate 11. The tip 24b of the upper clip piece 24 and thetip 25b of the convex curved portion 25a of the lower clip piece 25 areinclined to each other in an opening manner. Due to this, a guidingfunction is provided in inserting the head substrate 11 into the channelgroove-shaped fixation member 21.

The cover member 22 extends from the upper end of the positioning wall23 in a gentle, upwardly convex manner toward the first longitudinaledge 11a of the head substrate 11 by a predetermined length (long enoughto completely cover the drive ICs 13). In the illustrated embodiment,the cover member 22 of the protection cover 20 extends over theprotection coating 18 enclosing the drive ICs 13 so that a clearance isprovided above the protection coating. Therefore, instead of adopting ahard material such as an epoxy resin described above, a soft materialsuch as silicon resin may be usable for the protection coating 18.

On the other hand, the protection cover 20 is preferably formed by asuitable resin such as polypropylene or ABS resin containing 5-20% ofcarbon, so that a resistance of about 8-12MΩ is provided. In such aninstance, the protection cover 20 is electrostatically conductive.

As shown in FIGS. 1 and 2, the attachment of the protection cover 20 isperformed by bringing the channel groove-shaped fixation member 21 intoclipping engagement with the second longitudinal edge 11b of the headsubstrate 11. At this time, the clipping operation can be easilyperformed, since the second longitudinal edge 11b of the head substrate11 is guided by the flaringly inclining tips 24b, 25b of the respectiveclip pieces 24, 25 constituting the fixation member 21. In the assembledcondition, it is preferable to bring the lower clip piece 25 of thechannel groove-shaped fixation member 21 into contact with thesupporting member 19.

The minimum distance L between the two clip pieces 24, 25 in theoriginal state is smaller than the thickness L₂ of the head substrate11. Thus, in the assembled state, the two clip pieces 24, 25 are held inclipping engagement with the second longitudinal edge 11b of the headsubstrate 11 with a proper elastic clipping force. Therefore, theprotection cover 20 can be attached to the head substrate 11 with asufficient holding force without using other fixing means such as screwsor an adhesive. As a result, the assembling operation is facilitatedremarkably, and adaptation to automatic assembling is easily realized.

Since the channel groove-shaped fixation member 21 is directly broughtinto clipping engagement with the second longitudinal edge 11b of thehead substrate 11, as shown in FIG. 4, the positioning of the protectioncover 20 relative to the head substrate 11 is performed with greataccuracy. In particular, the cover member 22 can be positioned withgreat accuracy relative to the heating resistor 12.

As shown in FIG. 4, the transferring path of the recording paper P in aprinting unit utilizing the thermal printhead 10 is basically determinedby a platen roller R arranged in facing relation to the heating resistor12 on the head substrate 11. The position of the platen roller R isdetermined based on that of the heating resistor 12 on the headsubstrate 11. In the illustrated embodiment, the cover member 22 of theprotection cover 20 is positioned based on the head substrate 11, asdescribed above. Therefore, it is possible to arrange the cover member22 at an intended position with great accuracy relative to thetransferring path of the recording paper P. As a result, while unevencontact of the recording paper P with the protection cover 20 isminimized, the projection amount of the cover member 22 is maximized,thereby maximizing the protecting function for the drive ICs 13 and theguiding function for the recording paper P.

In the above embodiment, the protection cover 20, which is made of acarbon-containing synthetic resin, has an electrical conductivity of apredetermined resistance, and the head substrate 11 is mounted on theelectrically conductive supporting member 19 having a high thermalconductivity. Further, the lower clip piece 25 of the fixation member 21of the protection cover 20 is brought into contact with the supportingmember 19. Therefore, the static electricity generated on the recordingpaper P during e.g. high-speed printing is advantageously conducted tothe conductive supporting member 19 via the protection cover 20. Thus,the protection cover 20 is prevented from unduly causing electricalshort due to accumulated static electricity.

FIGS. 5 and 6 show a thermal printhead according to a second embodimentof the present invention. All the constituting elements except aprotection cover of the illustrated embodiment are identical to those ofthe first embodiment. Therefore the elements are designated by the samereference numerals and a detailed description is not given. Regardingthe designation of the constituting elements of the protection cover, aprime (') is added to the reference numerals used for the firstembodiment.

Similarly to the first embodiment, the protection cover 20' of thesecond embodiment includes a fixation member 21' having a positioningwall 23' and a pair of clip pieces 24', 25', and a cover member 22'formed integrally with the fixation member. However, in the secondembodiment, the cover member 22' of the protection cover 20' whenmounted on the head substrate 11 is elastically urged to be always heldin close contact with the surface of the protection coating 18 enclosingthe drive ICs 13. To this end, while it is necessary to arrange thecover member 22' of the protection cover 20' to be elasticallydeformable, the height of the cover member 22' in an original state needbe set smaller than the height of the protection coating 18 enclosingthe drive ICs 13. As already described, proper elasticity isadvantageously given to the cover member 22' by making the protectioncover 20' of a carbon-containing synthetic resin. In order to preventthe cover member 23' of the protection cover 20' from unfavorablyaffecting the drive ICs 13 due to the elastic deformation, theprotection coating 18 should be formed by a hard resin.

With the arrangement of the second embodiment, the cover member 22' ofthe protection cover 20' is elastically held in close contact with theprotection coating 18. Thus, it is possible to effectively avoid atransfer error of the recording paper P, which might be otherwise causedwhen the leading edge of the recording paper P enters a clearancebetween the cover member 22' and the protection coating 18.

FIGS. 7-9 show a thermal printhead according to a third embodiment ofthe present invention. The constituting elements except a protectioncover of the illustrated embodiment are identical to those of the firstembodiment. Therefore, the same reference numerals are used and adetailed description is not given.

The protection cover 20" of the third embodiment includes a fixationmember 21" for fitting engagement to the circumference of a thermalprinthead 10 constituted by a supporting member 19 and a head substrate11 carried thereby, and a cover member 22" extending above the drive ICs13. More specifically, the fixation member 21 is made in the form of anelongated rectangular frame, which includes a positioning wall 23" heldin direct contact with the entire length of the second longitudinal edge11b of the head substrate 11, a front engagement wall 25" held in directcontact with the entire length of the longitudinal edge 19a of thesupporting member 19, and a pair of side walls 26" connectingcorresponding ends of the front engagement wall 25" and the positioningwall 23". The positioning wall 23" is provided with a step portion 24"coming into engagement with the upper surface of the head substrate 11along the second longitudinal edge 11b of the head substrate 11. Thecover member 22" extends forward from the upper end of the positioningwall 23".

Similarly to the first embodiment, it is preferable that the protectioncover 20" is integrally formed by a suitable resin such as polypropyleneor ABS resin containing 5-20% of carbon, so that the cover has aresistance of about 8-12MΩ for example.

The fixation of the protection cover 20" having the above arrangement isprovided by fitting the entirety of the thermal printhead 10 into theframe-shaped fixation member 21", as shown in FIG. 7. In the assembledstate of the protection cover 20", the front engagement wall 25" of thefixation member 21" is brought into engagement with the edge 19a of thesupporting member 19. The heating resistor 12 on the head substrate 11is positioned based on the edge 19a. Thus, the cover member 22" formedintegrally with the fixation member 21" can be accurately positionedrelative to the edge 19a of the supporting member 19 and to the heatingresistor 12 on the head substrate 11. Particularly, the positioning wall23", to which the cover member 22" is directly connected, comes intoengagement with the second longitudinal edge 11b of the head substrate11. As a result, the cover member 22" is accurately positioned relativeto the heating resistor 12 and the platen R.

As shown in FIG. 9, the transferring path of the recording paper P in aprinting unit utilizing the thermal printhead 10 is determined by aplaten R arranged in facing relation to the heating resistor 12 on thehead substrate 11. The position of the platen R is determined so thatthe platen is brought into exact facing relation to the heating resistor12 on the head substrate 11. In the third embodiment, the cover member22" of the protection cover 20" is disposed at a relatively accurateposition relative to the heating resistor 12 on the head substrate 11.Therefore, the cover member 22" is also disposed at a relativelyaccurate position relative to the platen R in the printing unit. Sincethe cover member 22" of the protection cover 20" is accuratelypositioned, the projection amount of the cover member 22" can berendered as large as possible. Thus, a sufficient amount of overhangingis ensured for the mounting regions of the drive ICs 13, therebyoptimizing the protecting function by the protection cover 20 for thedrive ICs 13. Further, the attaching operation is remarkablyfacilitated, since the protection cover 20" is easily attached byfitting the frame-shaped fixation member 21" around the thermalprinthead.

The protection cover 20", when made by a carbon-containing syntheticresin, is given electrical conductivity of a proper resistance. In suchan instance, since the fixation member 21" of the protection cover 20"is always fitted around the conductive supporting member 19, the staticelectricity generated at the recording paper is properly conducted tothe supporting member 19 via the protection cover 20". As a result, thedrive ICs 13 on the head substrate 11 are advantageously prevented frombeing broken or damaged due to the static electricity, while theprotection cover 20" is prevented from unduly causing electrical short.

FIG. 10 shows an arrangement of a thermal printhead according to afourth embodiment of the present invention. Regarding the constitutingelements of the illustrated embodiment except a protection cover, theyare identical to those of the first embodiment. Thus, the same referencenumerals are used, and a detailed description is not given for them.

Similarly to the third embodiment, the protection cover 20"' of thefourth embodiment includes a frame-shaped fixation member 21"' which hasa positioning wall 23"' formed with a step portion 24"', a frontengagement wall 25"' and a pair of side walls 26"', and a cover member22"' formed integrally with the fixation member. However, in the fourthembodiment, the cover member 22"' of the protection cover 20"', whenmounted on the head substrate 11, is always elastically urged into closecontact with the surface of the protection coating 18 enclosing thedrive ICs 13. To this end, the cover member 22"' of the protection cover20"' need be rendered elastically deformable, while the height of thecover member 22"' in an original state should be smaller than the heightof the protection coating 18 enclosing the drive ICs 13. As alreadydescribed, the cover member 22"', when made of a carbon-containingsynthetic resin, is advantageously given suitable elasticity. Theprotection coating 18 should be made of a hard resin to prevent thedrive ICs 13 from being unfavorably affected due to the elasticdeformation of the cover member 22"' of the protection cover 20"'.

In the fourth embodiment, the cover member 22"' of the protection cover20"' is elastically urged into close contact with the protection coating18. Thus, similarly to the second embodiment, a transferring error iseffectively eliminated by preventing the leading edge of the recordingpaper P from entering an otherwise present clearance between the covermember 22"' and the protection coating 18.

It is apparent that the scope of the present invention is not limited tothe embodiments described above. For instance, the heating resistor of athermal printhead may be of a thin film-type other than a thickfilm-type described above. Further, any protection cover is usable, asfar as the positioning relative to the head substrate 11 is performed bythe direct contact with the second longitudinal edge 11b of the headsubstrate 11.

I claim:
 1. A thermal printhead comprising:an insulating head substratehaving a first edge and a second edge opposite to the first edge; aheating resistor formed on the head substrate along the first edge; atleast one drive IC mounted on the head substrate along the second edge;and a protection cover mounted for covering the drive IC; wherein theprotection cover includes a cover member for covering the drive IC and afixation member formed integrally with the cover member, the fixationmember having a positioning wall coming into direct contact with thesecond edge of the head substrate; wherein the fixation member of theprotection cover comprises a channel groove having a pair of elasticallydeformable clip pieces projecting from the positioning wall toward thehead substrate, a minimum distance between the clip pieces in anoriginal state being smaller than a thickness of the head substrate sothat the second edge of the head substrate is clipped by the clippieces; and wherein one of the clip pieces has a flat contact surfaceheld in surface contact with an obverse surface of the head substrate,the other clip pieces having a convexly curved portion held in contactwith a reverse surface of the head substrate.
 2. The thermal printheadaccording to claim 1, further comprising an electrically conductivesupporting member having a high thermal conductivity, the head substratebeing mounted on the electrically conductive supporting member, theprotection cover being electrostatically conductive, a portion of thefixation member of the protection cover contacting the supportingmember.
 3. The thermal printhead according to claim 2, wherein theprotection cover is integrally formed by a carbon-containing syntheticresin.
 4. The thermal printhead according to claim 1, wherein the driveIC on the head substrate is enclosed by a hard protection coating thecover member of the protection cover being elastically deformable andheld elastically in contact with the protection coating.
 5. A thermalprinthead comprising:an electrically conductive supporting member havinga high thermal conductivity; an insulating head substrate mounted on theelectrically conductive supporting member, the head substrate having afirst edge and a second edge opposite to the first edge; a heatingresistor formed on the head substrate along the first edge; at least onedrive IC mounted on the head substrate along the second edge; and aprotection cover mounted for covering the drive IC; wherein theprotection cover includes a cover member for covering the drive IC and afixation member formed integrally with the cover member, the fixationmember having a positioning wall coming into direct contact with thesecond edge of the head substrate; and wherein the fixation member ofthe protection cover comprises a frame which includes an engaging frontwall coming into engagement with an edge of the supporting memberadjacent to the heating resistor, and a pair of side walls connectingthe engaging front wall to the positioning wall.
 6. The thermalprinthead according to claim 5, wherein the positioning wall includes astep portion engaging the obverse surface of the head substrate adjacentthe second edge of the head substrate.
 7. The thermal printheadaccording to claim 5, wherein the protection cover is electrostaticallyconductive.
 8. The thermal printhead according to claim 7, wherein theprotection cover is integrally formed by a carbon-containing syntheticresin.
 9. A protection cover mounted on a thermal printhead including aninsulating head substrate having a first edge and a second edge oppositeto the first edge, a heating resistor formed on the head substrate alongthe first edge, and at least one drive IC mounted on the head substratealong the second edge, the protection cover comprising:a cover memberfor covering the drive IC, and a fixation member formed integrally withthe cover member, the fixation member having a positioning wall cominginto direct contact with the second edge of the head substrate; whereinthe fixation member of the protection cover comprises a channel groovehaving a pair of elastically deformable clip pieces projecting from thepositioning wall in a same direction as the cover member, a minimumdistance between the clip pieces in an original state being smaller thana thickness of the head substrate so that the second edge of the headsubstrate is clipped by the clip pieces; and wherein one of the clippieces has a flat contact surface held in surface contact with anobverse surface of the head substrate, the other clip piece having aconvexly curved portion held in contact with a reverse surface of thehead substrate.
 10. The protection cover according to claim 9, whereinthe cover is integrally formed by a carbon-containing synthetic resin.11. The protection cover according to claim 9, wherein the cover memberis elastically deformable.
 12. A protection cover mounted on a thermalprinthead which includes: an electrically conductive supporting memberhaving a high thermal conductivity; an insulating head substrate mountedon the electrically conductive supporting member, the head substratehaving a first edge and a second edge opposite to the first edge; aheating resistor formed on the head substrate along the first edge; andat least one drive IC mounted on the head substrate along the secondedge; the protection cover comprising:a cover member for covering thedrive IC, and a fixation member formed integrally with the cover member,the fixation member having a positioning wall coming into direct contactwith the second edge of the head substrate; wherein the fixation memberof the protection cover comprises a frame which includes an engagingfront wall coming into engagement with an edge of the supporting memberadjacent to the heating resistor, and a pair of side walls connectingthe engaging front wall to the positioning wall.
 13. The protectioncover according to claim 12, wherein the positioning wall includes astep portion which engages the obverse surface of the head substrateadjacent the second edge of the head substrate.